ADEN, Yemen (Reuters) - Yemeni armed forces killed an al Qaeda commander from Uzbekistan and at least 12 other militants in fighting in south Yemen on Thursday, the third day of an offensive against the Islamist group, local military and security sources said.

The Uzbek citizen, known as Abu Muslim al-Uzbeki, died during fighting in the province of Abyan, the source told Reuters. On Tuesday, President Abd Rabbu Mansour Hadi said 70 percent of al Qaeda fighters in Yemen were foreigners.

Al Qaeda in the Arabian Peninsula (AQAP) and its offshoot, Ansar al-Sharia, have hampered the U.S.-allied country's efforts to restore stability since a popular uprising in 2011 that forced a change in government.

Hundreds of people have died in bombings, suicide attacks and raids by the militant group against military and government facilities and foreign nationals.

Stability in Yemen, which shares a long border with the world's top oil exporter Saudi Arabia, became an international concern in recent years after AQAP tried to carry out attacks abroad, including an attempt blow up a U.S.-bound airliner.

Since 2012, AQAP's main base has been Abyan's mountainous al-Mahfad area, where militants fled after the army, with U.S. help, drove them from towns and areas they had seized during the chaotic uprising against then-President Ali Abdullah Saleh.

Yemeni troops launched their offensive into an expanse of south Yemen spanning 20,000 square km (7,700 square miles) - the size of the U.S. state of New Jersey - on Tuesday, backed by air force planes and hundreds of local militiamen.

MILITANT TRAINING CAMPS HIT

A Yemeni official and a tribal source told Reuters that the head of the AQAP cell in al-Mahfad, Ali bin Lakraa', had died of wounds inflicted during air strikes that targeted militant training camps in al-Mahfad last month.

"His cell was the most active of AQAP and Ansar al-Sharia in Yemen. That cell launched multiple operations that targeted the military and oil and gas facilities," the official said.

A local tribal source described Lakraa' as "one of the most high profile and active al Qaeda leaders in Abyan and Shabwa provinces".

The state news agency Saba said the army had directed "painful blows" to militants in al-Mahfad. The battle was being overseen by the defense minister himself, it said.

However, independent media outlets from south Yemen suggest the army was encountering stiff resistance from militants and is suffering heavier losses than the government is ready to admit.

The Aden al-Ghad newspaper described the fighting near al-Mahfad as "vicious" and published what it said were exclusive photos of burnt-out of armored vehicles.

Saba also said that the governor of al-Bayd province, Al-Dhaheri al-Shaddadi, and the head of the southern military command, Major General Ali Muhsen Muthana, survived an ambush on Thursday, but three of their guards were killed.

The Defence Ministry's newspaper, 26 September, said on its website that six of the attackers died in clashes after the ambush while returning to al-Bayda after inspecting some military positions.

So far around 18 al Qaeda fighters and eight Yemeni soldiers have been killed during the military operation since Tuesday, according to local officials and state media.